1. Field of the Invention
This invention generally relates to a method and apparatus for tensioning a chain saw and more particularly to a method and apparatus for quickly and easily increasing the tension on the chain of a chain saw to maintain proper tension on the chain.
2. Description of the Prior Art
In the operation of a chain saw the chain extends around the drive shaft and the chain saw blade. It is necessary for the chain to be properly tensioned. If the tension on the chain is either in excess or insufficient, the life of the chain can be greatly shortened. Additionally, excess or insufficient tension can result in problems associated with broken chains and/or disattachment of the chain from the saw, both of which can potentially seriously injure an operator of a chain saw.
During use of the chain saw, the chain tension changes because the link pivots wear, and, accordingly, the chain tends to lengthen over its life. Thus, it is important for a chain saw to include means to quickly, easily and properly apply tension to the chain. Past efforts in this area have provided cumbersome devices that are unable to accurately tension the chain without overtensioning the chain. These efforts are outlined in the following patents:
Smith, U.S. Pat. No. 830,860 discloses a chain saw having a frame comprising two flat mating solid sides and a track having straight edges and inwardly-curved ends fixed therebetween to form a chamber for storing oil for lubricating the track. A rotatable shaft is mounted to the frame on adjustable bearings and supported by brackets attached to the frame by set screws for adjusting the shaft relative to the frame and saw for regulating the tension of the saw on the track.
Strunk, U.S. Pat. No. 2,765,821 discloses a chain saw blade tensioning device rigidly adjustably securing the saw blade to the frame. The frame is provided with a pair of bosses which support a pair of studs in a mutually spaced relation. The studs may receive nuts which, when tightened, rigidly adjustably secure the saw blade in fixed relation to the frame. The saw blade may be adjusted relative to the chain sprocket to tension the chain by means of a take-up device which includes a shiftable rigid plate having an elongated slot. The plate member includes an adjusting screw for shifting of plate with respect to the frame. Tensioning of the saw is accomplished by loosening nuts on the studs, then turning the adjusting screw to shift the saw blade outwardly in the frame.
Adams, U.S. Pat. No. 2,767,746 discloses a chain tightener for a powered chain saw comprising a bolt having one end interconnected with the chain saw cutting bar and the other end extending into the frame member. A nut is positioned on the bolt. When the nut is tightened, the bar is shifted outwardly with respect to frame to tighten the chain.
Mall, U.S. Pat. No. 2,910,099 discloses an auxiliary take-up handle for a chain saw having an idler roller. The device includes an adjustment means to lengthen or shorten the guide bar for adjusting the tension of the saw chain. In order to tension the chain, the handle is turned to thread adjusting member along the shaft position of the handle to move the idler assembly away from the guide bar to tension the chain. Also provided within the handle is a coil spring for preventing over tensioning of the chain and for acting as a shock absorber and accepting abnormal loads.
Walker, U.S. Pat. No. 2,194,284 discloses a tension adjusting means for tensioning a chain saw comprising a cutting bar attached to a frame by means of a pair of spaced studs. The cutting bar includes on the elongated slot through which the studs extend. The frame includes a slot member having a ribbed portion which receives a screw and a nut having a projecting lug. A coil spring is positioned between the nut and the lug. The lug bears against an aperture in the bar to urge the bar towards its distal end.
Progl, U.S. Pat. No. 3,866,320 discloses a chain saw with a convenient means for adjusting the tightness of the chain on the guide bar comprising an adjusting screw for moving the guide bar of a chain saw away from the frame to tension the chain. The adjusting screw is rotatable by a member that extends outside of the cover which may be easily accessed by an operator. The rotatable member is connected to the adjusting screw by an angle drive means.
Kerrison, U.S. Pat. No. 4,223,438 discloses a direct bar oiler for chain saws. The device includes a bolt with a traveling block positioned thereabout. The bolt extends through a groove that receives the traveling block. Rotation of the bolt moves the traveling block along the groove. The traveling block has a finger which engages the aperture in the chain bar for moving the chain bar with respect to the frame to tension the chain.
Nagashima, U.S. Pat. No. 4,835,868 discloses a chain saw tensioner having a threaded rod member received in a hole of the frame and a pin member screwed onto the threaded rod member. A portion of the rod member extends through a lateral guide slot and into a slot formed in the chain guide bar whereby when the threaded rod member is rotated, the pin member moves in the axial direction of the threaded rod member to move the chain guide bar with respect to the frame tension the saw chain.
Scott et al., U.S. Pat. No. 4,316,327 discloses a chain saw with a tension adjustment screw engaging the rearward end of the saw bar mounted on the frame of the saw, at the rear thereof, for accessibility.
Schliemann et al., U.S. Pat. No. 4,999,918 discloses a chain saw with a chain tensioning device for adjusting the tensioning force of the chain. The guide bar is clamped to the housing at one end thereof. For tensioning the chain, the guide bar is movable along a longitudinal direction when the clamping piece is loosened.
Martenson, U.S. Pat. No. 5,177,871 discloses a belt tension system for power tool comprising a frame, an arm, a means for affixing the arm to the frame, and a means for moving the arm relative to the frame. Means for adjusting tension includes a driven gear, a drive gear perpendicular to the driven gear, a visual tension indicator connected to the driven gear, and a spring. The drive gear has helical threads adapted to engage the threads on the driven gear in order to tension the belt. A bolt that attaches the arm to the frame is loosened and the spring biases the arm forward to further adjust the tension. A screwdriver is used to rotate the drive gear which coacts with the driven gear to rotate a threaded shaft to increase the tension.
Edlund, U.S. Pat. No. 5,070,618 discloses a guide bar for a chain wherein the guidebar is moveable with respect to the body of the chain saw, thereby moving the blade of the chain saw with respect to the body to tension the chain comprising a cog wheel interconnected with the shaft extending through a fitting hole in the guidebar. Also included is a cup spring on the shaft between the cog wheel and a plate for preventing self turning of the shaft. Also included are two guide bar bolts with nuts. The tightening of the nuts compresses the cup spring to lock the cog wheel in its set position.
Horne, U.S. Pat. No. 4,315,370 discloses a chain saw with a chain bar having a chain and a lever for moving the chain bar to tension the chain and a bolt for fastening the cutter bar in a desired position.
Leighton, U.S. Pat. No. 4,563,817, discloses a chain saw bar having a base end with an elongated slot including a ratchet end crawl structure carried at the base end of the bar. The ratchet and crawl structure enables lengthwise adjustment of the bar. The ratchet and crawl structure includes ratchet teeth and a clamp plate facing the ratchet teeth including resilient crawl members for engagement with the ratchet teeth.
Edlund, U.S. Pat. No. 4,920,650, discloses a tension arrangement for a chain saw in which the chain saw sword is secured to the saw body with a bolt and is displaceable along its longitudinal axis by means of a tension screw.
Talberg, U.S. Pat. No. 5,174,029, the chain saw includes a distal portion of a blade that is slidable with respect to the base portions. The means are provided for extending the distal portion of the cutting bore relative to the base portion.
None of these prior efforts, taken either alone or in combination, teach or suggest all of the elements or the advantages of the present invention. Particularly, none of these patents teach a way to quickly, easily and accurately tension a chain for a chain saw, without overtensioning the chain.